Abstract   

    Pedigree, breeding and performance records of a purebred Sahiwal herd maintained at Livestock Experiment Station, Jahangirabad, Khanewal during the period 1939-97 were utilised for the present study. The effect of inbreeding on various performance traits was studied using a fixed effect model with inbreeding and other effects, viz, year and season of birth as independent variables, The two sets of analyses were carried out, one with cows classified as either inbred (F>O) or non-inbred (F=O), and other with. inbreeding coefficients as a covariate to estimate change in performance per unit (%) increase in inbreeding coefficient. The analyses were carried out by least squares technique, The pedigree analysis revealed that there was a decreasing trend in the average level of inbreeding in the present herd. The coefficient of inbreeding among the 503 inbred animals was 3.25 percent, the highest level being 26.78 percent. The number of sires used was 213 out of which 27 were inbred with average inbreeding coefficient 3.125 percent. Only 2 sires were having coefficient of inbreeding 25 percent or more. One of the main reasons for this low level of inbreeding in the herd was incompleteness of pedigrees especially for animals born in the earlier years of period under study. Although, there was a slight inbreeding depression in most of the traits but effect of inbreeding on all the performance traits was non-significant statistically more precise pedigree recording and planned mating strategies be adopted to avoid adverse inbreeding effects. It is signified that in future.    

Key words: Inbreeding depression, Pedigree, Sahiwal.